1. Field of the Invention
The invention relates to the field of data storage libraries and, in particular, to improved accessors and rails for data storage libraries.
2. Statement of the Problem
Data storage libraries provide a cost effective way of storing large amounts of data. Data storage libraries may use magnetic tape, magnetic disks, optical tape, optical disk, etc, as the storage media for data. A data storage library that uses magnetic tape is referred to as a tape library. A typical tape library includes a plurality of storage shelves for storing tape cartridges. The tape library may vary in size from storing a few tape cartridges to storing thousands of tape cartridges. The storage shelves comprise multiple columns and rows of storage slots for storing tape cartridges. The tape cartridges are readable and writeable by one or more tape drives in the tape library. One or more robotic accessors are used to transport tape cartridges between the storage shelves and the tape drives. Accessors are also referred to as robotic pickers, robotic arms, etc. The movements of the accessors are controlled by a library control unit.
To access a selected file stored in the tape library, a host computer contains information from which it can map a particular file to the tape cartridge on which the file is stored. The host computer transmits a command to the tape drive. The tape drive then transmits the command to the library control unit. Under control of the library control unit, an accessor is operable to locate a particular tape cartridge on the storage shelves, retrieve the tape cartridge from a storage shelf, transport the tape cartridge to a tape drive, and insert the tape cartridge into the tape drive. The tape drive then reads data from or writes data to the magnetic tape of the tape cartridge. After use of the tape cartridge is finished, the accessor is operable to remove the tape cartridge from the tape drive, transport the tape cartridge to the appropriate storage shelf, and return the appropriate tape cartridge to the storage shelf.
FIG. 1 illustrates a tape library 100 comprising a single storage frame 102 in the prior art. A storage frame comprises a section or module having a certain number of storage shelves having slots to store media cartridges, such as tape cartridges. Storage frame 102 includes a plurality of storage shelves 104-105 having slots for storing tape cartridges. Storage shelves 104 are on a front wall of storage frame 102, and storage shelves 105 are on a back wall of storage frame 102. Storage frame 102 also includes a plurality of tape drives 106 for reading data from or writing data to the tape cartridges stored in the storage shelves 104-105. Storage frame 102 also includes an accessor 108.
Accessor 108 is operable to transport tape cartridges between the storage shelves 104-105 and the tape drives 106. Accessor 108 comprises a gripper assembly 112 for gripping one or more tape cartridges and transporting the tape cartridges between the storage shelves 104-105 and tape drives 106. The gripper assembly 112 is mounted to a vertical rail 114 (also referred to as a Y-rail) and may be moved to different vertical positions on the Y-rail 114 via a Y-rail drive 116 to access tape cartridges on different rows of the storage shelves 104-105. The Y-rail drive 116 may comprise a motor turning a lead screw. The vertical rail 114 and gripper assembly 112 may be transported horizontally along a horizontal rail 118 (also referred to as an X-rail) by an X-rail drive 120. The X-rail 118 is mounted between the storage shelves 104-105 to allow the accessor 108 to travel between the storage shelves 104-105. The gripper assembly 112 may rotate approximately 180 degrees via a rotational drive 122 to access the storage shelves 104 on the front wall, and the storage shelves 105 and tape drives 106 on the rear wall.
FIG. 2 illustrates an X-rail drive 120 for accessor 108 in the prior art. The other elements of accessor 108 are not shown, but would be connected to X-rail drive 120 and would extend upward out of the top of page in FIG. 2. X-rail drive 120 includes a drive motor 202 connected to a drive pulley 204 via a belt 206. Drive pulley 204 is connected to a pinion (not visible) by a shaft. The pinion engages a rack 210 of X-rail 118. When drive motor 202 turns drive pulley 204, drive pulley 204 turns the pinion on rack 210 to move accessor 108 in the X-direction. Guide rollers 216 for X-rail drive 120 engage a guide rod 218 of X-rail 118 to guide accessor 108 when moving in the X-direction.
FIG. 3 illustrates a tape library 300 comprising multiple storage frames 102 in the prior art. In order to increase the size of tape library 100, additional storage frames 102 are bolted onto the original storage frame 102 (see FIG. 1) to form a linear chain of storage frames 102. Tape library 300 formed of multiple storage frames 102 may include at least two accessors.
FIG. 4 is a top view of tape library 300 in the prior art. In FIG. 4, the storage frames 102 are connected side-by-side to form a linear chain. The storage shelves 104-105 are aligned respectively to form two rows of storage shelves. The X-rails 118 for each storage frame 102 are connected to one another so that the accessors (ACC) 108 (shown in FIG. 4 as boxes for illustrative purposes) may share a common X-rail 118 and access tape cartridges in any of the storage frames 102.
One problem with the tape library 300 shown in FIGS. 3-4 is that the tape library 300 can only grow in one linear direction. The tape library 300 thus has a long, narrow footprint that may not work for the room or building housing the tape library 100. One major limitation in how a tape library can grow is the X-rail 118 and the X-rail drive 120 of the accessor 108. Due to the configuration of the X-rail drive 120, the X-rail 118 needs to be a continuous rail and cannot branch off at angles, such as right angles. If an X-rail 118 were built with an angle, the X-rail drive 120 would not be able to negotiate the angle. Therefore, if the X-rail 118 needs to be continuous, then the shape of the tape library 300 is limited to a straight line, or a curved or circular configuration.
Another problem with the configuration of tape library 300 is that a maximum number of two accessors 108 can be used. If either accessor 108 in FIG. 4 becomes disabled, the other accessor can push the disabled accessor to one end of tape library 300 and out of the way. If a third accessor were to be added to tape library 300 and the middle accessor became disabled, then the disabled accessor would hinder access to certain storage shelves 104-105.
FIG. 5 is a top view of a single U-shaped storage frame 502 in the prior art. The U-shaped storage frame 502 includes outside storage shelves 504 and inside storage shelves 505. An accessor 508 is operable to access tape cartridges in storage shelves 504-505 by traveling along U-shaped rail 510. By using a U-shaped storage frame 502, the tape library can grow in two dimensions.
FIG. 6 is a top view of a tape library 600 using multiple U-shaped storage frames 502 in the prior art. To expand in one direction, other storage frames 602 may be bolted onto the legs of the U-shaped storage frame 502 to expand the tape library 600. The accessor 508 for U-shaped storage frame 502 can access the other storage frames 602 bolted onto the end of storage frame 502. To expand in another direction, multiple U-shaped storage frames 502 can be connected side-by-side with a pass-through mechanism 610.
There are multiple problems with this configuration. The U-shaped storage frame 502 has a large radius in the corners of the “U” which allows the accessor 508 to turn. However, the large curved areas make a region where tape cartridge density is sacrificed as rectangular tape cartridges cannot be most efficiently packed around a curve. Another problem is that the accessors 508 in one U-shaped storage frame 502 cannot access tape cartridges stored in another U-shaped storage frame 502, except through a pass-through mechanism 610. It is inefficient to use the pass-through mechanism 610 to pass tape cartridges from one U-shaped storage frame 502 to another, as several different accessors 508 need to handle the tape cartridges.
It would therefore be desirable to design a tape library, or other types of data storage libraries, that have angled rails and accessors that can negotiate the angled rails.